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1202

PEDDLE A N D TURNER: SOLUBILITIES OF SALTS OF

CXXV.-Solubilities of Salts of Ammonium Bases in Water and i n Chlorc@w'. Part 1; Solubility as a Constitutive Property. By CYRILJAMES PEDDLE and WILLIAMERNESTSTEPHEN TURNER. THE measurements recorded in this paper were prompted partly by observations we had previously made in connexion with the relation of the solubility of substances t o their state of molecular aggregation (Peddle aud Turner, T., 1911, 99,685; Turner, Zbid., 1911, 99, 880). It was pointed out in the second of the two communications referred t o that miscibility of two substances was pmsible when both were normal or both associated, but that solubility was limited when one substance was normal and the other associated; and in support of the rule various illustrations were given, both in connexion with the miscibility of liquids and the solubility of solids in liquids. I n addition to the evidence there quoted, certain other generalisations cocnecting the properties of molecular weight, solubility, and dielectric constant can be shown to lead to the view that the solubility of a substance should be connected with its degree of association. The first of these generalisations is that of Walden (Zeitsch. physikal. Chem., 1906, 55, 683) to the effect that the solubility of salts-similar in type to those we have employed-is greater the more highly associated the solvent. Two other generalisations, taken in conjunction, must also lead a t onc0 to t8hesame view. Of these two, the first is also due t o Walden (Zeitsch. physikal. Chem., 1908, 61, 633), and states that the solubility of a normal electrolyte (for example, tetraethylammonium iodide) is greater the higher the dielectric constant of the solvent. This result was established after the examination of thirteen organic liquids, and a quantitative relationship of an empirical character obtained, namely, that the ratio €1 S'p, where E is the dielectric constant of the liquid and p, the molecular solubility of the electrolyte, is a constant quantity. The second of the two generalisations is the well-known NernstThomson rule, which may be stated in the form that the molecular weight of a substance capable of association or dissociation is greater the smaller the dielectric constant (see Turner, Zoc. cit.). Hence, we expected to find a general connexion between the degree of association of a salt and its solubility in a given solvent.

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AMMONIUM BASES IN WATER AND I N CHLOROFOHM.

PAKT J.

1203

We may say a t once, however, that we have not, under the conditions of experiment described below, been able clearly to establish the connexion we sought. The data we have adduced, however, furnish information for the solution of several other interesting problems. I n the first place, the character of the salts used, derived in many cases either from isomeric bases or from homologues, makes it possible to ascertain whether any additive relationships can be discovered in connexion with solubility, or whether the property is a constitutive one. Moreover, the discovery of a non-ionising substance, like chloroform, as a solvent for salts is, in itself, important, in that it allows a comparison to be made of the properties of salt solutions in two media of quite opposite character. Walden’s work consisted in the examination of but few salts in a large number of liquids. The present investigation, on the other hand, deals with many salts, derived from the substituted ammonium bases and also triethylsulphonium iodide, and only two solvents, water and chloroform. We purpose making a comparison of several properties of solutions in these solvents, contrasting in this first paper the solubility data at a temperature of 2 5 O ; whilst in a second communication we hope to give the results of an investigation on the effect of the addition of a second salt on these solubilities. EXPERIMENTAL. The twenty-four substances used in the investigation include all types of substituted ammonium salts-chlorides, bromides, and iodides-salts of which the molecular weights in chloroform solution have been recorded in a former paper (Turner, Zoc. cit.). The method of carrying out the solubility determination differed somewhat according as the solvent was water or chloroform. I n both cases samples of the salts were thoroughly dried and finely powdered and analysed repeated1p.w a check on their purity and freedom from moisture. When water was the solvent, excess of the salt was stirred in a Jena test-tube with water redistilled from acidulated permanganate, until a constant concentration was attained, the temperature variation of the thermostat used being less than Oslo. The time required to reach constant concentration varied with the salt, but, with one or two exceptions, no measurement was accepted until the solution had been at least twenty-four hours in the bath, and stirred for a t least five. As a rule, the time was much longer. A quantity of the solution varying between 2 and 5 grams was then removed to a weighing bottle by means of a pipette, previously warmed to 60--80°, and provided with a plug of cotton-wool at the tip, and the precise weight of solution

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PEDDLE AND TURNER: SOLU3ILITIES OF SALTS OF

determined. After dilution to a known volume, the solution was analysed by Vo’lhard’s method by titration with silver nitrate and thiocyanate. The chloroform used was purified by allowing it to remain for many hours over concentrated sulphuric acid, washing repeatedly with water, drying over calcium chloride, and fractionating to twoor three-hundredths of a degree. Small, brown, stoppered bottles were used for the solubility determinations in chloroform in order to diminish the tendency t o decomposition which the bromides and particularly the iodides show when exposed, in this solvent, to the light. The mixture of salt and solvent was warmed t o about 40° and then allowed to remain for many hours (twenty-four to one hundred and ten) at 25O, with frequent agitation. The solution, removed and weighed as with aqueous solutions, was placed in a vacuum desiccator, the chloroform slowly removed, and the residue dissolved in water and titrated. With several chlorides, such as propylamine, isobutylamine, and isoamylamine hydrochlorides, which could be heated to l l O o without any decomposition, determinations of solubility were also made by evaporation. The substances are tabulated in series, and the solubility results are expressed under P as grams of salt dissolved by 100 grams of solvent, under lOOn / N as molecular percentage solubility, n representing molecules of solute, N of solvent. I n order t o avoid repetition at a later stage, we have also inserted i n the table the relative degrees of association of the various salts in chloroform solution at the common concentration of 25 milligram molecules per 100 grams of solvent. These factors, denoted by A , have been drawn from the measurements of one of us (Turner, T., 1911, 99, 880). The following notes should be made on certain of the solutions : A queozcs S o h t i o ns.-Several were slightly coloured through keeping for a prolonged time, the following solutions being slightly yellow or brown : ethylambe and diethylamine hydrochlorides ; diethylamine hydrobromide and tetraethylammonium bromide; diethylamino hydriodide ; propylamine and dipropylamine hydrochlorides ; triethylsulphonium iodide. Solutions of ethylamine hydrochloride and tetraethylammonium chloride were very viscous. (retrue thylam monium Iodide.-Walden (loc. cit .> quotes two eolubility values, namely, 32’9 and 31.44 grams per 100 grams of solution. Calculated on the same basis, our value is 31-0grams, corresponding with the lower figure. Since these results, which agree, his and our own, were obtained by employing different, processes, the lower number is probably correct.

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AMMONIUM BASES IN WATER AND IN CHLOROFORM.

PART' I.

1205

Solubilities zt 2 5 O in Water and in Chloroform. In water. h

100?L/h-. Substance. M. W. P. 13,24 *39.3 NH,Cl ............ 53.5 61 '83 279-9 NH,Et,HCl ...... 81 -5 52.45 NH,Pra,HCI ...... 95.5 278'2 37 '48 238.9 isoC,H,'N H,,HCl 109'5 28.16 192.2 isoC,H,;NH,,HCl 123.6 81'57 369'2 NHMe,,HCl ...... 81'5 38'06 NHEt,,HCl ...... 109.5 21 %3 165'3 NHPr,,HCl ...... 37'6 61'83 NH,Et,HCI 81'5 231 -7 38.06 NHEt,HCl ..... 109.5 137.0 17.94 NEt,,HCl ......... 137'6 15'35 141-0 NEt4,Cl ............ 165'6 14-16 NT4,Br ............ 97.96 *77*0 36'64 311-6 NHEt,,HBr ..... 154.0 14'91 150-6 NEt,,IiHr ......... 182-1 279.5 23'96 NEt, Hr ............ 210'1 33 -79 377.2 NHE&,HI ...... 201 -0 29-09 NEt,,HI 229 *O 370'0 3.15 45.0 NEt41 ............ 257'0 1-07 18-64 NPra41 ............ 313'1 0.03 0 "14 N(C,H,,),I ...... 425 -3 14.88 107.1 NH,Ph,HCl ...... 129'5 47.54 378-8 NHYhMe,HCl 143'5 6-35 50'6 CH,Ph'NH,,HCl 143.5 0.17 2.17 ~NH(CHzPh),,HCl233.6 0'03 0-61 '(N(CH,Ph),,HCl 323% 31-56 431'0 SEtJ ............... 246'1 18.99 301.3 C,H,*NEtI ...... 285 *O * These values have been obtained from the tables in Inorganic and Organic Substances."

......

.........

...

In chlaroform. h

P.

100nlN.'

A.

-

0'0 0 *17 5.26 11-56 5 -10 16'91

0.25 6.56 12-63 4'92 24.77

(8) 4'63 5 '92 3 -92

47.24

4098

-

2-11

29'45 17-37 8 '24 0'0 46.65 23'44 25-01 71-55 92'2 1*55 54.56 210.8

32.09 15.07 5 '93 0.0 36.11 15.37 14'21 42.50 48.05 0 '72 20-81 59.17

2-63 1-62 5-12

-

-

0 -0

0.37 11-41 47 -7 1.78 8eideII's

0'0

-

0 -0 0.19

-

-

-

1.78 7.2

__

2.52

-

4-40 2.17 -

-

-

4-21 1-26 23.14 7.6 0 '75 " Solubilities of

Tet raisoam ylam monizlm Iodide .-Solution difficult to titrate unless very dilute. Quinoline Ethiodide.-Solution dark red and oily. On addition of water, solution became viscid a t first, and a yellow deposit; appeared to be formed, but further addition of water gave a clear solution with only a slight yellow tinge. Chloroform Solutions.-Several substances gave yellow or brown solutions, but when evaporated the chloride and bromide residues were usually quite white. Tetraethylammonium iodide, quinoline ethiodide, and tetrapropylammonium iodide solutions were deep red. Tetraisoamylamhtonizlm Zod.ide.-Solution light yellow and viscous as glycerol. Solubility determined only by evaporation in a vacuum desiccator (ten weeks required for constancy of weight). Benzylamine Hydrochloride.-No weighable deposit from 7 grams of solution. Trib erwylamine Hydrochlorid e.-Solubility determined by evaporation, heating t o 1 loo, and placing under diminished pressure.

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PEDDLE AND TURNER: SOLUBILITIES OF SALTY OF

Triethy2sulphowiium Zodide.-This substance undergoes decomposition in chloroform. A solution of the salt, 0.6074 gram in 5 C.C. of chloroform, was allowed to remain for forty-three hours in the bath, and was then evaporated under diminished pressure, and the residue determined by titration. A loss of 22.2 per cent. of the salt was found t o have occurred. Two other solutions, a dilute and a concent-rated, were then prepared, and allowed t o remain at 25O for half an hour only, after which they were evaporated at the ordinary temperature and under diminished pressure. The first solution contained 0.5040 gram of salt in 6.3568 grams of solution (7.7 per cent.), the second 1.9976 grams in 5-1378 (39 per cent.). The residues determined by titration were 0.5044 gram and 1 *990 grams respectively.* Evidently no appreciable decomposition occurred during the process of evaporation, and the dry salt itself has also been found t o be quite stable under diminished pressure a t the ordinary temperature. Probably, theref ore, the figure quoted in the table does, or very nearly does, represent the actual solubility of triethylsulphonium iodide in chloroform. Discussion of Results.

Solubility in Water.

Great variation is exhibited in the solubilities of the salts, the mono- and di-substituted ammonium chlorides and triethylsulphonium iodide, for example, standing out in marked contrast with di- and tri-benzyl ammonium chlorides or tetraisoamylammonium iodide. The more important points are summarised as follows: (1) Substitution of a hydrogen atom i n an ammonium salt by an alkyl group very greatly increases the solubility (compare ammonium chloride, ethylamine hydrochloride, propylamine hydrochloride, etc.). Aromakic groups, such as the phenyl or benzyl group, are either much less effective in increasing t h e solubility or even decrease it;. The difference between the aliphatic and aromatic radicles is strikingly brought out by a comparison of aniline with methylaniline hydrochloride, the solubility of the Iatter being more than three times t h a t of the former. (2) When similarly constituted salts are compared, solubility in water decreases as the mass increases. It is only by confining the comparison most strictly to similar substances t h a t such regularity can be observed. The great difference between the 0ffect.a of aliphatic and aromatic radicles already discussed at once marks solubility as a highly constitutive property.

*

We are indebted to M. C. C. Bissett for making these experiments.

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AMMONIUM BASES IN WATER AND 1N CHLOROFORM.

PART J.

1207

An attempt has been made t o test whether any additive relations exist, since the substances examined are so related as make this comparison possible. Among the chlorides are four pairs of isomeric substances, namely, the hydrochlorides of ethylamine and dimethylamine ; of diethylamine and isobatylamine ; of triethylamine and dipropylamine; and of methylaniline and benzylamine. Only i n one case, the second mentioned, is there agreement between the values o f . molecular solubility, and in one case there is very wide divergence. Lack of agreement between isomerides, however, does not necessarily mean the absence of any additive relationships, as is well known. Comparing the homologues in the first three series in the table of solubilities, neglecting ammonium chloride, and making no comparison between n-propylamine and isobutylamine hydrochlorides, we have as differeqces between the members compared, in the first series 9-38 and 9.32; in the second, between salts of secondary amines, 2 x 21.75 and 2 x 8.2; in the third, 2 x 11.3, 2 x 10.1, and 2 x 1.3. These differences in the holecular solubility, set out in terms of a difference of composition of C’H,, do not raise any great hope of discovering additive relationships, although the persistent recurrence of an average difference value of about 9 units may not be without significance. Whatever t h e outcome of further and more exhaustive investigation of substances of precisely similar constitution, it is obvious that the solubility of salts in water must be written down as almost wholly, if not wholly, a constitutive property. (3) The constitutive character of solubility is also borne out in the effect exercised by the negative radicle, and it is not possible to say definitely whether the chloride, bromide, or iodide will have the greatest solubility in water. Solubility in Chloroform.

Compared in the usual sense (values of P),the salts appear to be distinctly less soluble in chloroform, on the whole, than in water. The surprising thing is t h a t they are so soluble. In most other organic solvenb of low dielectric constant, such as ether, benzene, carbon disulphide, carbon tetrachloride, and ethylene dibromide, their solubilities are exceedingly small, and from experiments we have carried out they are much more soluble in chloroform than in acetone. The magnitude of the solubility is all the more striking when reduced to terms of molecular solubility, when the it set, are b u t little less than in water ils solvent. numbers, taken Solubility in chloroform is therefore exceptional. It does not appear to depend on the fact that all the salts used in this investi-

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PEDDLE A N D TURNER: SOLUBILITIES OF SALTY OF

gation are haloids, for, from the experience of one of us, nitrates are likewise very soluble, and so also are various other salts containing still other negative radicles. There is no doubt that in this respect chloroform is a somewhat exceptional although at the same time a. valuable solvent. Compared with water, it is often to be found t h a t the greater the solubility in water the smaller it is in chloroform, and vice versa; b u t there are quite a number of exceptions. It is obvious that in comparing a series of salts, a point will be reached a t which solubility in water and i n chloroform will be nearly the same. This applies in all probability to the triethylamine salts, possibly also t o those of diethylamine, the solubilities of which in chloroform appear exceptionally high. Other points to which attention may be called briefly are: (1) As in water, so also in chloroform, the solubility of an ammonium salt is greatly increased by the introduction of organic radicles, the aliphatic again having a much greater effect than the aromatic. Although we have made no exact measurements with aniline and methylbniline hydrochlorides, we have found t h a t the former may be regarded as insoluble, whilst the latter is very soluble in chloroform. (2) As a rule, increase in molecular weight is accompanied by increase of solubility. This rule is only strictly preserved when series of similarly constituted salts are compared (compare, for example, the monoalkylamine and dialkylamine salts as two series, a8 also the tetraethyl-, propyl-, and isomyl-ammonium iodides). iso Amylamine hydrochloride is an exception even under these conditions. (3) No suggestion of additive relationships occurs either by a comparison of isomerides or of homologous substances. (4) With the exception of tetraethylammonium iodide, the order of increasing solubility is chloride, bromide, iodide, so far as investigated. The absence of any definite connexion between solubility in water and in chloroform and chemical composition of the above salts may well give rise t o the question as t o whether any physical property of either component of the solution may affect the extent to which miscibility may occur, and this leads back to one of the objects of the investigation, namely, the effect of molecular association on solubility. It is very possible t h a t this factor has an influence. I n the solid state these salts must be regarded as built up of complex molecula; in aqueous solution they appear dissociated, in chloroform strongly associated. Now in accordance with the rule mentioned in the

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AMMONIUM BASES IN WATER AND I N CHLOROFORM.

PART I.

1209

introduction, that two substances which are both associated will readily mix, it should be found that the strongly msociated salts should be the ones most soluble in water. A strict test of t h e rule requires a knowledge of the molecular state of the salt in saturated solution, and this is not known except in a few cases. The association factors for dilute solution do largely indicate t h e relative order of complexity for much stronger solutions, however, and, recognising this, the table on p. 1205 shows that the rule holds, generally speaking, although the order of association is in many cases not that of solubility. As t o solubility in chloroform, it can be pointed out that when similarly constituted salts, such it8 the monosubstituted amine salts, the disubstituted salts, and the tetraalky lammonium iodides are compared in series, then the solubility increases as the degree of association decreases. Some doubt may be felt as to the sufficiency of this illustration, and in view of the fact t h a t the iodides, the most associated salts, are in several cases nevertheless the most soluble, it must be admitted t h a t molecular association cannot be the deciding factor i n solubility. That it is a factor is probable from what has been said already, and in the series of monoalkylamine hydrochlorides, isoamylamine hydrochloride is abnormal in being more associated than isobutylamine hydrochloride, and, in conjunction with this, also has the smaller solubility, which is alm abnormal. If it be admitted t h a t molecular association is a factor affecting solubility, it is not unlikely t h a t if a solvent like ethyl alcohol be employed, which, one of us has found, neither permits either marked association nor ionisation, greater regularity might be found t o exist among the solubilities observed. W e hope further to discuss this point in a later communication, and to examine in some detail the relationship between solubility and dielectric constant and between dielectric constant and molecular weight, which, as already indicated in the introduction, suggest the connexion between molecular state and solubility. We desire t o express our thanks to the Research Fund Committee of the cihemical Society f o r a grant which defrayed much of the expense entailed by this investigation. THE GRAMMARSCHOOL, BARNSLEY.

THE UNIVEHSITY, SHEFFLELD.